High energy atomic layer etching

ABSTRACT

Methods and apparatus for performing high energy atomic layer etching are provided herein. Methods include providing a substrate having a material to be etched, exposing a surface of the material to a modification gas to modify the surface and form a modified surface, and exposing the modified surface to an energetic particle to preferentially remove the modified surface relative to an underlying unmodified surface where the energetic particle has an ion energy sufficient to overcome an average surface binding energy of the underlying unmodified surface. The energy of the energetic particle used is very high; in some cases, the power applied to a bias used when exposing the modified surface to the energetic particle is at least 150 eV.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of prior U.S. patent application Ser.No. 16/148,939, filed Oct. 1, 2018, which in turn claims benefit of U.S.Provisional Patent Application No. 62/569,443, filed Oct. 6, 2017, andtitled “PULSING ATOMIC LAYER ETCHING,” and U.S. Provisional PatentApplication No. 62/599,613, filed Dec. 15, 2017, and titled “HIGH ENERGYATOMIC LAYER ETCHING,” each of which is incorporated by reference hereinin their entireties and for all purposes.

BACKGROUND

Semiconductor fabrication processes include etching of variousmaterials. As three dimensional structures shrink towards a sub-10 nmnode, traditional etching processes face unprecedented challenges. Forexample, pitch loading becomes a concern as the etch rate is affected bythe increasing aspect ratio. The challenges associated with thetransport of neutrals and ions to the etch front, the surface reactionrate at etch fronts, and etch product removal from the etch front becomeprominent as devices shrink.

SUMMARY

Provided herein are methods and apparatuses for performing high energyatomic layer etching. One aspect involves a method of processing asubstrate, the method including: providing a substrate including amaterial to be etched; exposing a surface of the material to be etchedto a modification gas to modify the surface and for a modified surface;and exposing the modified surface to an energetic particle topreferentially remove the modified surface relative to an underlyingunmodified surface, the energetic particle having an ion energysufficient to overcome an average surface binding energy of theunderlying unmodified surface.

In various embodiments, the ion energy of the energetic particle issufficient to break bonds of the underlying unmodified surface. Theenergetic particle may be delivered in temporally separated doses havinga duty cycle between about 1% and about 10%.

In various embodiments, a bias voltage is applied to a substrate supportholding the substrate during the exposing the modified surface to theenergetic particle.

In some embodiments, the energetic particle removes an amount of themodified surface, and the amount of the removed modified surface isgiven by the equation

${\theta (t)} = {1 - {\exp \left( \frac{{- Y} \cdot F \cdot t}{d} \right)}}$

such that Y is ion yield of the energetic particle, F is flux ofenergetic particle, t is the duration of the exposure to the energeticparticle, and d is the surface density of material to be etched.

In various embodiments, the energetic particle does not significantlysputter the underlying unmodified material. For example, the modifiedsurface may be exposed to the energetic particle for a duration issufficient to remove the modified surface in a self-limited manner.

Another aspect involves method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and applying a biaswhile exposing the modified surface to an energetic particle to removethe modified surface, such that the power applied to the bias is atleast 150 eV.

In various embodiments, the power applied to the bias is at least 500eV.

Another aspect involves a method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and delivering a dose ofenergetic particle to the modified surface to remove the modifiedsurface, such that the dose is insufficient to remove the modifiedsurface when delivered using a bias voltage less than the surfacebinding energy of the underlying unmodified surface.

Another aspect involves a method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and exposing themodified surface to an energetic particle to preferentially remove atleast 80% of the modified surface relative to an underlying unmodifiedsurface for a duration greater than a duration sufficient to remove themodified surface and the underlying unmodified surface by ionbombardment.

Another aspect involves a method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and exposing themodified surface to an energetic particle in pulses having a duty cycleof less than 100%.

Another aspect involves a method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and exposing themodified surface to an attenuated dose of an energetic particle, suchthat the dose without attenuation has an energy greater than a surfacebinding energy for the material to be etched when delivered continuouslyto the modified surface.

In various embodiments, the dose is attenuated by varying the ion fluxof the activated species.

In some embodiments, the dose is attenuated by varying the duration ofthe modified surface being exposed to the activated species.

In various embodiments, the attenuated dose includes two or moretemporally separated pulses of the activated species to the modifiedsurface to remove the at least some of the modified surface.

In some embodiments, the dose is attenuated by varying the accelerationof ions in the activated species to the modified surface.

In various embodiments, the dose is attenuated by varying the biasvoltage applied to a substrate support holding the substrate fordirectionally delivering the activated species to the modified surface.

Another aspect involves a method of processing a substrate, the methodincluding: providing a substrate including a material to be etched;exposing a surface of the material to be etched to a modification gas tomodify the surface and form a modified surface; and exposing themodified surface to an energetic particle in temporally separatedpulses; and modulating the ion energy and dose during the temporallyseparated pulses. In some embodiments, modulating the ion energy anddose includes increasing the ion energy and compensating the increase ofion energy with reduced dose.

Another aspect involves a method of processing a substrate, the methodincluding: exposing the substrate to a modification gas to modify asurface of the substrate to form a modified surface; exposing themodified surface of the substrate to a removal gas; and providing aplurality of temporally separated pulses of energy generated from anactivation source during the exposing the modified surface to theremoval gas to remove at least some of the modified surface from thesubstrate.

In some embodiments, the method also includes repeating exposing thesubstrate to the modification gas and exposing the modified surface tothe removal gas in two or more cycles, such that the plurality oftemporally separated pulses of energy is provided during the exposingthe modified surface to the removal gas in each cycle.

In various embodiments, the plurality of temporally separated pulses ofenergy includes at least 100 temporally separated pulses of energy percycle.

In various embodiments, the temporally separated pulses of energy issufficient to remove the modified surface and insufficient to physicallysputter the modified surface.

In various embodiments, the energy provided is defined by a bias windowof a minimum voltage applied to the substrate during the exposure to theremoval gas sufficient to remove the modified surface, and a maximumvoltage applied to the substrate during the exposure to the removal gasinsufficient to sputter the modified surface.

In various embodiments, the plurality of temporally separated pulses ofenergy are pulsed at a frequency between about 10 Hz and about 200 Hz.

In various embodiments, the plurality of temporally separated pulses ofenergy are pulsed at a duty cycle between about 1% and about 10%.

In some embodiments, the activation source includes two or more sources.

In some embodiments, the activation source is selected from the groupconsisting of radio frequency plasma, bias applied to the substrate,ultraviolet radiation, photons, and combinations thereof.

In some embodiments, the activation source includes voltage applied tobias the substrate. The bias voltage may be at least between about 500 Vand about 1500 V. The bias may be pulsed between 0V and a bias voltagebetween about 500V and about 1500V.

In some embodiments, the bias is pulsed between a low bias voltagebetween about 100V and about 300V and a high bias voltage between about500V and about 1500V.

In some embodiments, the bias is pulsed using a pulsing frequencybetween about 10 Hz and about 200 Hz.

In some embodiments, the bias is pulsed using a duty cycle between about1% and about 20%.

In some embodiments, the activation source includes radio frequencyplasma.

In some embodiments, the radio frequency plasma is generated by applyinga power and the radio frequency plasma power pulsed between an OFF statewhere the plasma power is 0 W and an ON state where the plasma power isbetween about 50 W and about 900 W.

In some embodiments, the radio frequency plasma generated by applying apower and the radio frequency plasma power is pulsed between a lowplasma power and a high plasma power, the low plasma power being betweenabout 10 W and about 100 W and the high plasma power being between about900 W and about 1500 W.

In some embodiments, the radio frequency plasma is pulsed using apulsing frequency between about 10 Hz and about 200 Hz.

In some embodiments, duty cycle of the radio frequency plasma pulsing isbetween about 1% and about 20%.

In some embodiments, such that the activation source includes radiofrequency plasma and bias applied to the substrate. The bias may bepulsed between 0V and a bias voltage between about 500V and about 1500V.The bias may be pulsed between a low bias voltage between about 100V andabout 300V and a high bias voltage between about 500V and about 1500V.The radio frequency plasma may be generated by applying a power and theradio frequency plasma power pulsed between an OFF state where theplasma power is 0 W and an ON state where the plasma power is betweenabout 50 W and about 900 W. The radio frequency plasma may be pulsedbetween a low plasma power and a high plasma power, the low plasma powerbeing between about 10 W and about 100 W and the high plasma power beingbetween about 900 W and about 1500 W.

In various embodiments, the substrate includes one or more narrowfeatures and one or more wide features.

In some embodiments, the substrate is processed at a substratetemperature between about 0° C. and about 120° C.

In some embodiments, the substrate is processed in a process chamberhaving a chamber pressure between about 5 mTorr and about 1 Torr duringthe exposing the substrate to the modification gas.

In some embodiments, the substrate is processed in a process chamberhaving a chamber pressure between about 5 mTorr and about 200 mTorrduring the exposing the substrate to the removal gas.

Another aspect involves a method of processing a substrate, the methodincluding: exposing the substrate to a modification gas to modify asurface of the substrate to form a modified surface; exposing themodified surface of the substrate to a removal gas; and periodicallyigniting a plasma in two or more temporally separated pulses during theexposing of the modified surface to the removal gas to remove at leastsome of the modified surface from the substrate.

The method may also include repeating exposing the substrate to themodification gas and exposing the modified surface to the removal gas intwo or more cycles, such that the two or more temporally separatedpulses of plasma are provided during the exposing the modified surfaceto the removal gas in each cycle.

In some embodiments, the plurality of temporally separated pulses ofplasma comprise at least 100 pulses of energy per cycle.

The method may also include applying a bias in pulses during theexposing of the modified surface to the removal gas. In someembodiments, the method also includes repeating exposing the substrateto the modification gas and exposing the modified surface to the removalgas in two or more cycles, such that the two or more temporallyseparated pulses of plasma and bias are provided during the exposing themodified surface to the removal gas in each cycle.

In some embodiments, the plurality of temporally separated pulses ofplasma and bias comprise at least 100 pulses per cycle, a cycleincluding exposing the substrate to the modification gas and exposingthe modified surface to the removal gas.

In some embodiments, the plasma and bias are pulsed at the samefrequency.

In some embodiments, the plasma and bias are pulsed using the same dutycycle.

Another aspect involves a method of processing a substrate, the methodincluding: exposing the substrate to a modification gas to modify asurface of the substrate to form a modified surface; exposing themodified surface of the substrate to a removal gas; igniting a plasmaduring the exposing of the modified surface; and periodically applying abias in two or more temporally separate pulses to the substrate duringthe exposing of the modified surface to the removal gas to remove atleast some of the modified surface from the substrate.

The method may also include igniting a plasma in pulses during theexposing of the modified surface to the removal gas.

In some embodiments, the method includes repeating exposing thesubstrate to the modification gas and exposing the modified surface tothe removal gas in two or more cycles, such that the two or moretemporally separated pulses of bias power are provided during theexposing the modified surface to the removal gas in each cycle.

In some embodiments, the plurality of temporally separated pulses ofbias power comprise at least 100 pulses per cycle, a cycle includingexposing the substrate to the modification gas and exposing the modifiedsurface to the removal gas.

Another aspect involves apparatus for processing a substrate, theapparatus including: a process chamber including a showerhead and asubstrate support for holding the substrate having a material, a plasmagenerator, and a controller having at least one processor and a memory,such that the at least one processor and the memory are communicativelyconnected with one another, the at least one processor is at leastoperatively connected with flow-control hardware, and the memory storesmachine-readable instructions for: causing introduction of amodification gas to the process chamber; causing introduction of aremoval gas to the process chamber; and causing an activation source tobe pulsed during the introduction of the removal gas.

In some embodiments, the memory further stores machine-readableinstructions for causing pulse frequency of the activation source duringthe introduction of the removal gas to be between about 10 Hz and about200 Hz.

In some embodiments, the memory further stores machine-readableinstructions for causing duty cycle of the activation source during theintroduction of the removal gas to be between about 1% and about 10%.

In some embodiments, the activation source is a plasma generated in theprocess chamber using a plasma power and the memory further storesmachine-readable instructions for causing the activation source to pulsebetween an OFF state where the plasma power is 0 W and an ON state wherethe plasma power is between about 50 W and about 900 W.

In some embodiments, the activation source is a plasma generated in theprocess chamber and the memory further stores machine-readableinstructions for causing the activation source to pulse between a lowplasma power and a high plasma power, the low plasma power being betweenabout 10 W and about 100 W and the high plasma power being between about900 W and about 1500 W.

In some embodiments, such that the memory further storesmachine-readable instructions for causing a bias to be applied to thesubstrate support in pulses. For example, the memory may also storemachine-readable instructions for causing the bias to be pulsed between0V and a bias voltage between about 500V and about 1500V. In someembodiments, the memory further stores machine-readable instructions forcausing the bias to be pulsed at the same pulsing frequency as theactivation source. In some embodiments, the memory further storesmachine-readable instructions for causing the bias to be pulsed at thesame pulsing duty cycle as the activation source.

Another aspect may involve an apparatus for processing a substrate, theapparatus including: a process chamber including a showerhead and asubstrate support for holding the substrate having a material, a plasmagenerator, and a controller having at least one processor and a memory,such that the at least one processor and the memory are communicativelyconnected with one another, the at least one processor is at leastoperatively connected with flow-control hardware, and the memory storesmachine-readable instructions for: causing introduction of amodification gas to the process chamber; causing introduction of aremoval gas to the process chamber; and causing radio frequency plasmapower to be generated in the process chamber in two or more temporallyseparated pulses during the introduction of the removal gas.

In some embodiments, the memory further stores machine-readableinstructions for causing pulse frequency of the radio frequency plasmapower during the introduction of the removal gas to be between about 10Hz and about 200 Hz.

In some embodiments, the memory further stores machine-readableinstructions for causing duty cycle of the radio frequency plasma powerduring the introduction of the removal gas to be between about 1% andabout 10%.

In some embodiments, the memory further stores machine-readableinstructions for causing the radio frequency plasma power to pulsebetween an OFF state where the plasma power is 0 W and an ON state wherethe plasma power is between about 50 W and about 900 W.

In some embodiments, the memory further stores machine-readableinstructions for causing the radio frequency plasma power to pulsebetween a low plasma power and a high plasma power, the low plasma powerbeing between about 10 W and about 100 W and the high plasma power beingbetween about 900 W and about 1500 W.

In some embodiments, the memory further stores machine-readableinstructions for causing a bias to be applied to the substrate supportin pulses.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias to be pulsed between 0V and a biasvoltage between about 500V and about 1500V.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias to be pulsed between a low biasvoltage between about 100V and about 300V and a high bias voltagebetween about 500V and about 1500V.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias to be pulsed at the same pulsingfrequency as the radio frequency plasma power.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias to be pulsed at the same pulsing dutycycle as the radio frequency plasma power.

Another aspect involves an apparatus for processing a substrate, theapparatus including: a process chamber including a showerhead and asubstrate support for holding the substrate having a material, a plasmagenerator, and a controller having at least one processor and a memory,such that the at least one processor and the memory are communicativelyconnected with one another, the at least one processor is at leastoperatively connected with flow-control hardware, and the memory storesmachine-readable instructions for: causing introduction of amodification gas to the process chamber; causing introduction of aremoval gas to the process chamber; and causing bias power to be appliedto the substrate support in two or more temporally separated pulses tothe substrate during the introduction of the removal gas.

In some embodiments, the memory further stores machine-readableinstructions for causing pulse frequency of the bias power during theintroduction of the removal gas to be between about 10 Hz and about 200Hz.

In some embodiments, the memory further stores machine-readableinstructions for causing duty cycle of the bias power during theintroduction of the removal gas to be between about 1% and about 10%.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias power to pulse between an OFF statewhere the bias power is 0V and an ON state where the bias power isbetween about 500V and about 1500V.

In some embodiments, the memory further stores machine-readableinstructions for causing the bias power to pulse between a low biaspower and a high bias power, the low bias power being between about 100Vand about 300V and the high bias power being between about 500 V andabout 1500V.

In some embodiments, the memory further stores machine-readableinstructions for causing a plasma to be ignited by applying a plasmapower in pulses during the introduction of the removal gas.

In some embodiments, the memory further stores machine-readableinstructions for causing the plasma power to be pulsed between 0 W and aplasma power between about 50 W and about 900 W.

In some embodiments, the memory further stores machine-readableinstructions for causing the plasma power to be pulsed at the samepulsing frequency as the bias power.

In some embodiments, the memory further stores machine-readableinstructions for causing the plasma power to be pulsed at the samepulsing duty cycle as the bias power.

These and other aspects are further described below in conjunction withthe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows example schematic diagrams of substrates undergoing atomiclayer etching.

FIG. 2 shows a three-dimensional schematic view of a FinFETsemiconductor device.

FIGS. 3A and 3B are process flow diagrams depicting operations formethods in accordance with certain disclosed embodiments.

FIGS. 4A-4G are timing schematic diagrams depicting examples ofoperations performed in accordance with certain disclosed embodiments.

FIG. 4H is a timing schematic diagram of example low energy and highenergy ALE techniques.

FIGS. 4I and 4J are example schematic diagrams of low and high ionenergy removal of a modified layer in ALE.

FIG. 5 is a schematic diagram of an example process chamber forperforming disclosed embodiments.

FIG. 6 is a schematic diagram of an example process apparatus forperforming disclosed embodiments.

FIG. 7 is a graph of etch per cycle of silicon on insulator as afunction of bias power used in pulsed ALE where bias power is pulsed foran experiment conducted in accordance with certain disclosedembodiments.

FIG. 8A is a graph of etch per cycle of amorphous silicon and siliconoxide as a function of bias power used in pulsed ALE where bias power ispulsed for an experiment conducted in accordance with certain disclosedembodiments.

FIG. 8B is a graph of etch selectivity as a function of bias power usedin pulsed ALE where bias power is pulsed for the experiment conductedwith respect to FIG. 8A.

FIG. 9A is a graph of etch per cycle of amorphous silicon and siliconoxide as a function of bias power used in pulsed ALE where bias power ispulsed for an experiment conducted in accordance with certain disclosedembodiments.

FIG. 9B is a graph of etch selectivity as a function of bias power usedin pulsed ALE where bias power is pulsed for the experiment conductedwith respect to FIG. 9A.

FIGS. 10A and 10B are graphs of pitch loading as a function of trenchcritical dimension used in pulsed ALE for different bias powers for anexperiment conducted in accordance with certain disclosed embodiments.

FIG. 11 is a graph depicting etch per cycle of material used pulsed ALEversus ALE without pulsing.

FIG. 12A is graph of an example etch per cycle model based on a functionprovided in Eqn. 5B.

FIG. 12B is a graph of etch per cycle as a function of argon bias in anexample of low energy ALE.

FIG. 13 is an example of ion energy as a function of “on” time for argonexposure for complete removal.

FIG. 14A is an example of normalized etch per cycle for ALE as afunction of bias for various “on” times of argon exposure for pulsedALE.

FIG. 14B is a graph of example etch per cycle for “on” times of argonexposure for simulated and experimental data.

FIG. 15 is a graph of example etch rates for various argon bias voltagesfor silicon and SiCl.

FIG. 16A is an example drawing of a substrate exposed to 50V argon biasin an experiment.

FIG. 16B is an example drawing of a substrate exposed to 200V argon biasin an experiment.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Semiconductor processing often involves various etching operations. Oneexample technology for processing and forming 3D structures involvesreactive ion etch (RIE), which generates directional etch and sidewallpassivation. In general, RIE generates reactive species such ashalogen-containing species generated from fluorine-containing compounds,chlorine, hydrogen bromide; and ions such as helium and/or argon to usein directional etching, and various species to passivate sidewallsurface. However, as etch depths increase, depth loading for features ofdifferent aspect ratios occurs, in part due to the species hittingsidewalls of the feature holes as the species are delivered to thebottoms of the features. Depth loading also occurs due to the variety ofiso areas (such as features having a wide feature opening) and denseareas (such as features having a narrow feature opening). A featurehaving a “narrow” opening may be defined as a feature having an openingdiameter or line width less than that of a “wide” feature in relativeterms. Wide features may have an opening diameter or a criticaldimension at least 1.5 times, or at least 2 times, or at least 5 times,or at least 10 times or more than 10 times larger than the criticaldimension of narrow features. Examples of “narrow” features includefeatures having an opening diameter between about 1 nm and about 10 nm.Examples of “wide” features include features having an opening diameteron the order of hundreds of nanometers to about 1 micron.

Etching processes often involve exposing a material to be etched to acombination of etching gases to remove the material. However, suchremoval may not be self-limiting and in some cases may etch more thandesired, or result in an undesirable feature profile. As feature sizesshrink, there is a growing need for atomic scale processing such asAtomic Layer Etch (ALE). ALE is a technique that removes thin layers ofmaterial using sequential self-limiting reactions in cycles of nominallyself-limiting steps that result in digital and small changes in filmthicknesses. The process is characterized by smoothness andconformality, and also directionality in the case of some ALE.

ALE can be used in advanced semiconductor manufacturing (e.g. technologynode of less than about 10 nm) for the blanket removal orpattern-definition etching of ultra-thin layers of material with atomicscale in-depth resolution and control. Generally, ALE may be performedusing any suitable technique. Examples of atomic layer etch techniquesare described in U.S. Pat. No. 8,883,028, issued on Nov. 11, 2014; andU.S. Pat. No. 8,808,561, issued on Aug. 19, 2014, which are hereinincorporated by reference for purposes of describing example atomiclayer etch and etching techniques. In various embodiments, ALE may beperformed with plasma, or may be performed thermally.

ALE may be performed in cycles. The concept of an “ALE cycle” isrelevant to the discussion of various embodiments herein. Generally anALE cycle is the minimum set of operations used to perform an etchprocess one time, such as etching a monolayer. The result of one cycleis that at least some of a film layer on a substrate surface is etched.Typically, an ALE cycle includes a modification operation to form areactive layer, followed by a removal operation to remove or etch onlythis modified layer. The cycle may include certain ancillary operationssuch as sweeping one of the reactants or byproducts. Generally, a cyclecontains one instance of a unique sequence of operations. As an example,an ALE cycle may include the following operations: (i) delivery of areactant gas, (ii) purging of the reactant gas from the chamber, (iii)delivery of a removal gas and an optional plasma, and (iv) purging ofthe chamber. In some embodiments, etching may be performednonconformally. FIG. 1 shows two example schematic illustrations of anALE cycle. Diagrams 171 a-171 e show a generic ALE cycle. In 171 a, thesubstrate is provided. In 171 b, the surface of the substrate ismodified. In 171 c, the next step is prepared. In 171 d, the modifiedlayer is being etched. In 171 e, the modified layer is removed.Similarly, diagrams 172 a-172 e show an example of an ALE cycle foretching a silicon film. In 172 a, a silicon substrate is provided, whichincludes many silicon atoms. In 172 b, reactant gas chlorine isintroduced to the substrate which modifies the surface of the substrate.The schematic in 172 b shows that some chlorine is adsorbed onto thesurface of the substrate as an example. Although chlorine is depicted inFIG. 1, any chlorine-containing compound or suitable reactant may beused. In 172 c, the reactant gas chlorine is purged from the chamber. In172 d, a removal gas argon is introduced with a directional plasma asindicated by the Ar⁺ plasma species and arrows, and ion bombardment isperformed to remove the modified surface of the substrate. Ionbombardment in low energy ALE is performed continuously, and at processconditions that prevent the substrate from sputtering. For example,during this operation, a bias is applied to the substrate to attractions toward it. The bias power is typically set to a power that preventssputtering since the power is continuously delivered during this removaloperation. Thus, the power applied to the bias is typically on the orderof less than about 100 V. The bias power depends on the material to beetched, so for example, for germanium, the bias power may be betweenabout 20 V and about 35V, while for silicon, the bias power may bebetween about 35 V and about 65 V. In these examples, germanium wouldsputter at bias powers greater than 35 V, and silicon would sputter atbias powers greater than 65 V. Accordingly, bias power is typically keptlow to prevent sputtering, and also prevent damage to the substrate andsurrounding materials. The minimum bias power in these example “biaswindows” are the minimum bias power needed to provide enough energy tothe substrate to remove the modified material. Thus, at bias powers lessthan 20 V for germanium or less than 35 V for silicon for continuouslydelivered bias power, the modified surface will not have enough energyto be removed from the substrate. In 172 e, the chamber is purged andthe byproducts are removed.

A cycle may only partially etch about 0.1 nm to about 50 nm of material,or between about 0.1 nm and about 20 nm of material, or between about0.1 nm and about 2 nm of material, or between about 0.1 nm and about 5nm of material, or between about 0.2 nm and about 50 nm of material, orbetween about 0.2 nm and about 5 nm of material. The amount of materialetched in a cycle may depend on the purpose of etching in aself-limiting manner. In some embodiments, a cycle of ALE may removeless than a monolayer of material.

ALE process conditions, such as chamber pressure, substrate temperature,plasma power, frequency, and type, and bias power, depend on thematerial to be etched, the composition of the gases used to modify thematerial to be etched, the material underlying the material to beetched, and the composition of gases used to remove the modifiedmaterial. However, the combination of these factors make performing ALEfor etching a variety of materials challenging.

Performing ALE in a self-limiting manner without sputtering for avariety of materials is challenging and is often limited by certainprocess conditions as bias power is typically kept low to preventsputtering and damage to the substrate.

As feature sizes shrink to less than 10 nm in feature width, a 1 nmcritical dimension variation between features causes large fluctuationof the aspect ratio from feature to feature, and a depth loading effectis observed in etch processes conducted by traditional ALE withcontinuous bias (low energy ALE). During etch processes, the etch amountper cycle of ALE of material in a deeper trenches is less than the etchamount per cycle of ALE of material in a shallower trench. In somecases, the etch amount per cycle can be less at the bottoms of featuresthan at the top near the feature opening, even within a single feature.Without being bound by a particular theory, it is believed that tosatisfy the self-limiting characteristic of ALE in extreme 3Dstructures, the ion energy supplied from the plasma would need to bealtered. However, for substrates having features of various aspectratios, if an ion energy were selected such that it was sufficient toetch features having a large feature opening using ALE, features havingnarrower feature openings will receive ions having reduced energy andflux, thereby being inefficient in etching the smaller features.However, if a greater ion energy were selected to effectively etch thefeatures having narrow feature openings, the larger features wouldexperience much higher ion energy, which would thereby sputter thesurfaces of the larger features, eliminating the self-limiting aspect ofALE. This depth loading effect manifested in 3D structures suggests thatetch rate depends on the geometry of features.

There are several reasons why there may be geometric dependence duringetching. One example challenge that may be present is a charging effectwhich occurs where due to the generation of positive ions, there is someaccumulation of such positively charged ions at or near the featureopenings of high aspect ratio features due to the narrow featureopening, thereby resulting in a charged differential within the depth ofthe feature where the feature opening is more positively charged thanthe bottom of the feature, which results in a repelling phenomenonbetween the incoming positively charged ions used to remove the modifiedsurface and the positively charged feature opening, thereby resulting inuneven removal of the modified surface at the bottom of the feature.

Given the increasing number of new materials being introduced intointegrated circuit processing and the large number of combinations ofprocess parameters (gas pressure, wafer temperature, plasma power, ionenergy, etc.), achieving an ALE process that does not sputter but alsoetches in a layer-by-layer self-limiting way for a given material whileavoiding the charging effect in high aspect ratio features ischallenging.

Provided herein are methods of performing controlled atomic layeretching using high energy. Disclosed embodiments involve exposing asurface of material to be etched to a modification gas to modify thesurface and form a modified surface and exposing the modified surface toan energetic particle to remove the modified surface relative to anunderlying unmodified surface, the energetic particle having an ionenergy sufficient to overcome an average surface binding energy of theunderlying unmodified surface.

For example, a substrate may include a material to be etched, thematerial having an average surface binding energy. The material to beetched includes various layers of material. Given the self-limitingaspect of atomic layer etching, during the exposure to the modificationgas, the modification gas modifies the surface of the material to beetched such that the exposed surface is modified, but an underlyingmaterial is not modified. When the modified material is exposed to anenergetic particle, such as an ion, electron, neutron, photon, or otherspecies, the energetic particle removes the modified surface, leavingbehind the underlying unmodified surface, and maintaining theself-limiting aspect of ALE. The energetic particle is delivered withhigh energy, which may be an ion energy sufficient to overcome anaverage surface binding energy of the underlying unmodified surface ofmaterial to be etched. That is, in some embodiments, if the energeticparticle were delivered to the surface in large doses, such as manyenergetic particles all at once, the energetic particle would break thebonds of the underlying material, thereby sputtering the material underthe modified surface and minimizing the self-limiting aspect of ALE. Incontrast, disclosed embodiments involve modulating the energy of theenergetic particle with the dose for delivering the energetic particlesuch that high energy is compensated by delivering a small dose. In lowenergy ALE, low energy is compensated by delivering a high dose; thatis, energetic particles are delivered with low energy but can bedelivered continuously in high doses and still remove only the modifiedsurface without affecting the underlying unmodified surface to maintaina self-limiting aspect of ALE. However, in high energy ALE, high energyis compensated by delivering a low dose; that is, an energetic particleis delivered with high energy which would be much greater than energyused in low energy ALE (and would remove more than the modified surfaceif delivered in the same dose as in low energy ALE) but in a low dosesuch that the etching is still self-limiting.

Various embodiments involve modifying a surface of material to be etchedand exposing the modified surface to an attenuated dose of activatedspecies generated from activating a removal gas to remove some, or allof the modified surface. An attenuated dose can be achieved using avariety of ways. One way to provide an attenuated dose of the activatedspecies is to deliver the activated species in temporally separatedpulses, which may involve pulsing plasma power, bias voltage, gas flows,or more, in synchronous or asynchronous manners between high/low as wellas on/off processes. An attenuated dose is defined as delivering reducedeffect of a dose having an energy greater than a sputter thresholdenergy for the material to be etched when delivered continuously to themodified surface. In some cases, the sputter threshold is the surfacebinding energy of the material to be etched.

Another way to deliver an attenuated dose is by varying ion flux ofactivated species, whereas a dose without attenuation would have anenergy greater than the surface binding energy. Yet another example ofdelivering an attenuated dose is by varying the duration for which themodified surface is exposed to the attenuated dose of activated species.The duration can be insufficient to remove the modified surface. Forexample, a single pulse for a given duration of the attenuated dose maybe insufficient to remove the modified surface, but two or more pulsesfor the same duration delivered in an attenuated dose over time may besufficient to remove the modified surface. Another example involvesdelivering an attenuated dose by varying the acceleration of ionsgenerated in the activated species to the modified surface. Anotherexample involves delivering an attenuated dose by varying the biasvoltage applied to a substrate support holding the substrate fordirectionally delivering the activated species to the modified surface.In some embodiments, the attenuated dose is sufficient to remove themodified surface without sputtering underlying unmodified material.

Previous techniques for performing ALE were based on obtaining a “ALEwindow” of bias voltage applied to a substrate support holding thesubstrate during the removal operation of ALE to provide sufficientenergy to the modified surface to remove the modified surface moleculesfrom the substrate (the lower limit of the ALE window) but provide lessthan a threshold energy of the modified surface which, if exceeded,would result in physical sputtering of the material and/or the surfaceunderlying the modified surface (the upper limit of the ALE window).Such techniques focused on providing low bias voltage and low plasmapowers to prevent sputtering of the material on the surface to ensureremoval by ALE was self-limiting and can therefore be controlled in alayer-by-layer process.

In contrast, disclosed embodiments involve operating high plasma powers,high bias voltages, or both. It will be understood that the terms “biaspower” and “bias voltage” are used interchangeably herein to describethe voltage for which a substrate support is set when a bias is appliedto the substrate support. A threshold bias power or threshold biasvoltage refers to the maximum voltage of the bias applied to a substratesupport before material on the surface of a substrate on the substratesupport is sputtered. The threshold bias power therefore depends in parton the material to be etched, the gas used to generate plasma, plasmapower for igniting the plasma, and plasma frequency. Bias power or biasvoltage as described herein is measured in volts, which are indicated bythe unit “V” or “Vb”, where b refers to bias. Electron volts (eV) asdescribed herein is the amount of energy one electron acquires byaccelerating through a potential difference of 1 Volt. Electron voltsrefer to the amount of energy one electron acquires by acceleratingthrough a potential difference of 1 Volt. Disclosed embodiments canoperate at low duty cycle pulses, such as duty cycles between 1% and10%. Disclosed embodiments overcome the charging concern because thehigh energy delivered to the activated removal gas is sufficient toovercome the repelling effect. Although in low energy ALE one couldenvision trying to use a higher bias power to overcome the repellingeffect, higher bias power in low energy ALE will result in sputtering ordamage to the substrate due to long exposure time, thereby losing theself-limiting feature of ALE. In contrast, using pulsed ALE at highenergy overcomes the repelling effect while maintaining theself-limiting characteristic of ALE without sputtering.

As shown in FIG. 13 which is further described below, it is typicallyexpected that with a short duty cycle, removal of the modified layer isincomplete.

However, disclosed embodiments involve using short duty cycles as onetechnique for performing ALE using high energy. Without being bound by aparticular theory, it is believed that there is a time dependencerelated to the removal operation of ALE.

Let this example involve a silicon surface modified by chlorine plasmaand the modified surface having SiCl which can be removed using argonplasma. It will be understood that this is provided as only one example,but that the below representations are relevant to any suitable materialfor etching by any suitable plasma (in lieu of chlorine) and energeticspecies (in lieu of argon plasma) for ALE generally, including both lowenergy and high energy ALE.

Let N₀ represent the total number of surface sites on a substrate. Thetotal number of surface sites is given by:

N ₀ =N+S  Eqn. 1

where and N represents the total number of unreacted sites (sites forwhich SiCl remains on the surface), and S represents the total number ofreacted sites (sites where there is only the underlayer of Siremaining).

The reaction for desorbing chlorine onto the substrate is given by

Si—Si_(Cl)(s)+Ar+ions→Si(s)+SiCl(g)  Eqn. 2

This equation depicts ion-assisted desorption, and assumes no reversereaction with rate efficiency Y=yield, in reactions per ion.

Let F be the flux of ions given in ions/cm²-sec.

The rate of expression is therefore given by

$\begin{matrix}{{rate}_{rxn} = {{\frac{d}{dt}\lbrack S\rbrack} = {{Y \cdot F \cdot \lbrack N\rbrack} = {Y \cdot F \cdot \left( {\left\lbrack N_{0} \right\rbrack - \lbrack S\rbrack} \right)}}}} & {{Eqn}.\mspace{14mu} 3}\end{matrix}$

The derivation of [S] is given by the following expression at time t,assuming k is dependent of [S] and t:

$\begin{matrix}{{\int_{0}^{{\lbrack S\rbrack}_{t}}\frac{d\lbrack S\rbrack}{\left\lbrack N_{0} \right\rbrack - \lbrack S\rbrack}} = {{\int_{0}^{t}{{YFdt}\lbrack S\rbrack}_{t}} = {\left\lbrack N_{0} \right\rbrack \left( {1 - e^{- {YFt}}} \right)}}} & {{Eqn}.\mspace{14mu} 4}\end{matrix}$

The fractional surface reacted is given by θ as follows:

$\begin{matrix}{{{\theta (t)} \equiv \frac{\lbrack S\rbrack_{t}}{\left\lbrack N_{0} \right\rbrack}} = \left( {1 - e^{- {YFt}}} \right)} & {{{Eqn}.\mspace{14mu} 5}A} \\{{\theta (t)} = {1 - {\exp \left( \frac{{- Y} \cdot F \cdot t}{d} \right)}}} & {{{Eqn}.\mspace{14mu} 5}B}\end{matrix}$

Eqn. 5A is rewritten as Eqn. 5B. In Eqn. 5B, θ(t) represents the removalamount as a function of time, where Y(ε) is the ion yield for removing aproduct (0.1 ion at 0 eV, whereby Y(ε)˜√{square root over(ε_(i))}−√{square root over (e_(th))}), d is the surface density inunits of 1/cm2, F is the ion flux, which in some apparatuses may be˜1E16/cm²s at 50 eV, and t is the “on” time of argon ions, such as a 0.2second dose for 10% duty cycle of a 2 second operation.

FIG. 12B, which is later described below, shows an example of etch percycle using this inverse relationship function of Eqn 5A for ALE ofsilicon. Without being bound by a particular theory, it is believed thatfewer ions are needed at higher energy due to momentum transfer beingmore efficient at higher energy. An example is provided in the FIGS. 4Iand 4J. In FIG. 4I, low ion energy of 50 eV delivered to a modifiedsurface removes the modified surface using argon delivered at a velocityof 13000 m/s, where Y˜0.1 SiClx/ion. In comparison, in FIG. 4J, high ionenergy of 300 eV delivered to a modified surface removes the surfaceusing argon delivered at a velocity of 33000 m/s, where Y˜0.5 SiClx/ion.Thus, for a surface that needed 10 ions to remove using low ion energy,only two ions are needed to remove the same surface using high ionenergy.

Without being bound by a particular theory, while sputtering increaseswith ion energy, the SiCl surface etches faster than the underlying Sisurface, and thus the contribution to the etch amount is small until thereactive layer is removed. If the exposure time is very short, then thereactive layer is present for the majority of the removal time. Forexample, FIG. 15 shows an example of etch rate versus argon bias wherebySiCl etches faster (1501) than Si (1502) at all energies.

FIG. 16A shows an example of low energy ALE with 50V bias at 1.5seconds/cycle, which results in smoother surfaces, larger exposure timewindow, and more resolution per cycle, which can result in less damageto the underlayer. The grey represents TEOS on the substrate. The greenpresents the underlying material. FIG. 16B shows an example of the samesubstrate structure exposed to pulsed ALE using high energy, whichresults in higher throughput using similar synergistic effects, improvedaspect ratio dependent etching (ARDE) due to narrower ion angulardistribution function (IADF) given by 8° at 50 eV as opposed to 2° at500 eV, less charging effect, and less re-deposition and ion scattering.High energy ALE can be delivered in short pulses which may be useful foruse in CCP reactors. High energy ALE allows for a larger ion energywindow.

Disclosed embodiments are suitable etching a variety of materials,including metals, metal-containing materials, dielectric materials,semiconductor materials, insulating materials, and more. Non-limitingexamples include silicon, silicon oxide, silicon nitride, tungsten,carbon, germanium, metal oxides, and metal nitrides (such as titaniumnitride, aluminum nitride, etc.). While examples provided herein aredirected to etching silicon, it will be understood that disclosedembodiments can be used to etch a variety of materials, and modificationgas chemistry, removal gas chemistry, and process conditions may dependon the material to be etched.

Methods and apparatuses herein are directed to performing high energyatomic layer etching. High energy atomic layer etching (high energy ALE)can be used by compensating high energy with low dose. In contrast,conventional ALE performed at lower energy (low energy ALE) involves lowenergy with high dose. Dose is defined as the number of ions used duringthe removal operation of ALE.

In some embodiments, high energy ALE can be performed using an etchprocess referred to herein as pulsed atomic layer etching. In somecases, the terms “high energy ALE” and “pulsed ALE” are usedinterchangeably. A single high energy ALE cycle includes at least twooperations: 1) surface modification in continuous or pulsing plasma; and2) removal of the modified surface using one or more pulsed energysources, such as bias power, or radio frequency plasma power, or both,or photon energy, to remove the modified layer. Multiple pulses may beused in any of the surface modification and/or removal operations in asingle high energy ALE cycle. For example, in some embodiments, 100 ormore pulses of bias power pulsing may be performed during removal.During the removal, either the bias or the power or both may be pulsed,and in some cases, other energy may be used, such as photonic energy.Pulses may be synchronous or asynchronous when using both bias andplasma power pulsing. Frequencies for the pulsing may be the same ordifferent. Pulsing conditions, including pulsing on/off or between lowand high powers or voltages, frequency of pulses, duty cycle of pulses,and duration of pulses, may be carefully tailored depending on themodification chemistry, removal gas chemistry, material to be etched,substrate feature profile, and application of the disclosed embodiments.

Disclosed embodiments can be performed in a high energy ALE regime usingbetween about 10 times and about 20 times higher ion energy than lowenergy ALE processes. Some embodiments are performed by synchronizedpulsing of power of an inductively coupled plasma and bias to thesubstrate applied by delivering a voltage to the substrate at very lowduty cycles being between about 1% and about 10%. The new process regimeallows one to etch extremely narrow features with high aspect ratios,such as greater than about 30:1, with low loading effect and reduced oreliminated lateral etch.

Pulsed ALE may involve both pulsing plasma and ions bias pulsing suchthat pulsing is performed both during modification and removal.

Pulsing during surface modification can control effective plasma timeand be tailored to the apparatus or tool used to perform themodification. Pulsing during removal can be used to remove the modifiedsurface using high energy. In some embodiments, pulsing during removalmay include both pulsing RF plasma and pulsing bias power, and pulsingmay be synchronized such that RF plasma power pulsing and bias powerpulsing are pulsed at the same pulsing frequency and using the same dutycycle.

Pulsed ALE using pulsed energy provides a way to extend theself-limiting synergy window. Synergy means that favorable etchingoccurs due to interaction of both the surface modification and theremoval operations. The extended synergy window to a higher bias/energyregime can compensate the ion energy/flux loss reaching the etch frontdue to ion scattering associated with extremely narrow 3D structures.Thus, high energy ALE provides an operating regime allowing the sameetch per cycle in self-limiting reactions for a wide spectrum ofcritical dimensions and aspect ratios.

High energy ALE extends the self-limiting energy window for the synergybehavior of atomic layer etching. In continuous ion bombardment, thesputter threshold voltages of silicon for example may be greater than100V. That is, at bias powers greater than 100V, the silicon surfacewill sputter. Pulsing mode generates plasma and ions at a givenfrequency and duty cycle. With power/bias pulsing at lower duty cycle,the threshold sputter bias can be increased to a higher bias power.Thus, bias pulsing increases range and the magnitude of theself-limiting energy window by at least one order of magnitude comparedto low energy ALE.

Without being bound by a particular theory, it is believed that pulsedatomic layer etching is achieved due to the reduced ion fluence withpulsing. Given that fluence equals flux times time, it represents thedose of ions. As the simplest estimate, the reduction in dose can becalculated by the duty cycle and the ratio of step times. For example,for a 10% duty cycle, whereby the dose time is 2 seconds instead of 5seconds with the pulsing, then the effective reduction in fluence is94%. Thus, in this example, the wafer is exposed to 0.06 times theoriginal ion dose used in low energy ALE. The etched amount per cycledepends on ion dose and ion energy. In general, reducing the dose willresult in lower etch amount. Without being bound a particular theory, itis believed that the lower dose can be compensated by going to higherion energy

Compared with reactive ion etching, high energy ALE employs twoself-limiting steps to control the transport of reactants, and surfacereaction independently. The pulsing bias mode redefines theself-limiting window for ALE to provide a regime for etching 3Dstructures by ALE where bias power or RF power is independent of trenchsize and aspect ratio. Provided embodiments are suitable for etchingboth on blanket and patterned substrates. In some embodiments, the biaswindow for high energy ALE may have non-sharp maximum values, such thatthe maximum bias voltage used for high energy ALE without causingsputtering is a range of values, rather than a single set value.

Disclosed embodiments expand the ALE energy window, which is referred toas a range of voltage whereby etching is substantially self-limiting. Insome embodiments, the ALE energy window is determined by evaluating etchper cycle versus voltage graph and in some embodiments involvesidentifying where etch per cycle is a plateau and the energy window iscalculated as ± about 10% of the plateau value. In some embodiments,this can be performed by determining the inflection points at which apositive slope becomes a slope of 0 (a minimum), and a slope of 0becomes a positive slope (a maximum). In some embodiments, the ALEenergy window is a range of voltage that can be applied to the substrateto remove the modified surface of material without sputtering thesubstrate. The range of voltage includes a minimum voltage, which is theminimum voltage needed to provide enough energy on the modified surfaceto remove the modified material and a maximum voltage, which is themaximum voltage the substrate can withstand before the removal gassputters the substrate.

In low energy ALE, bias windows are typically narrower in the range ofbias voltages tend to be lower to prevent damage to the substrate causedby sputtering. By altering the duty cycle and therefore changing theduration of the applied energy to the removal gas, as the duty cycledecreases and thus as the duration of exposure to the energy decreases,the bias windows increase in range and in amplitude such that the biasvoltages that can be applied to the substrate can be up to 10 to 20times greater than the bias voltages used during low energy ALE. It maygenerally be expected that using greater energy on the removal gasduring removal would result in more damage, and thus one would try tomitigate damage by reducing the amount of energy by reducing biasvoltage or RF plasma power. However, without being bound by a particulartheory, it is believed that the amount of energy expended over time foreach set of modification chemistry, removal gas chemistry, and substratematerial chemistry is used to provide a bias window for removingmodified material. In low energy ALE, a certain limitation on bias poweris observed to prevent sputtering. However, in high energy ALE, the biaspower can be up to 10 or up to 20 times greater than the bias power usedin low energy ALE since the bias is delivered over time in pulses. Notethat while high energy ALE is performed in pulses, in some embodimentsother techniques may be used to deliver high energy during ALE. Whilelow energy ALE at bias powers that are used for high energy ALE wouldresult in sputtering, high energy ALE separates out the high bias powerover time, thereby preventing any sputtering on the substrate. Thecombination of energy applied and time (e.g., duty cycle) and flux, asdependent on the modification chemistry, removal gas chemistry, andmaterial to be etched, can be modified to maximize the bias window usingcertain disclosed embodiments.

Disclosed embodiments may be particularly suitable for etching featuresfor FinFET applications. FIG. 2 shows an example FinFET structure(fin-shaped field effect transistor) 200. Substrate 202 may be asemiconductor substrate. In this structure, surfaces 214 a and 204 acorrespond to source regions, while 214 b and 204 b correspond to drainregions. Liner 212 separates the semiconductor material of substrate 202from the insulator material 230 such as silicon oxide. Thin gatedielectric layers 206 b and 206 a may be deposited over the insulatormaterial 230 and may separate the insulator material 230 from the gate,which includes spacers 210, gate electrode 208, and gate electrodebarrier 208 a. Electrical contact 250 is formed over the top of thegate. Certain disclosed embodiments can be used to define thefin/shallow trench isolation with minimum depth loading for trenchesformed in substrate 202. Additionally, certain disclosed embodiments maybe suitable for dummy gate removal for gate electrode deposition.

FIGS. 3A and 3B are process flow diagrams depicting operations inmethods that are performed in accordance with certain disclosedembodiments. Operations in FIGS. 3A and 3B may be performed at a chamberpressure between about 1 mTorr and about 100 Torr, e.g., about 1 mTorrand about 1 Torr, such as about 50 mTorr. Operations in FIGS. 3A and 3Bmay be performed at a substrate temperature between about 0° C. andabout 120° C.

For the following discussion it will be understood that operations 302,304, 306, 310, and 312 of FIG. 3A may correspond to and/or be the sameas operations 302, 304, 306, 310, and 312 of FIG. 3B. In operation 302,a substrate is provided to a process chamber. The substrate may be asilicon wafer, e.g., a 200-mm wafer, a 300-mm wafer, or a 450-mm wafer,including wafers having one or more layers of material such asdielectric, conducting, or semi-conducting material deposited thereon. Apatterned substrate may have “features” such as vias or contact holes,which may be characterized by one or more of narrow and/or re-entrantopenings, constrictions within the features, and high aspect ratios. Thefeatures may be formed in one or more of the above described layers. Oneexample of a feature is a hole or via in a semiconductor substrate or alayer on the substrate. Another example is a trench in a substrate orlayer. In various embodiments, the feature may have an under-layer, suchas a barrier layer or adhesion layer. Non-limiting examples ofunder-layers include dielectric layers and conducting layers, e.g.,silicon oxides, silicon nitrides, silicon carbides, metal oxides, metalnitrides, metal carbides, and metal layers.

In some embodiments, the substrate does not have any features and thesurface of the substrate is a blanket layer of material. In someembodiments, the substrate includes features of various sizes. Invarious embodiments, types of substrates fabricated from performingdisclosed embodiments may depend on the aspect ratios of features on thesubstrate prior to performing disclosed embodiments. In someembodiments, features on a substrate provided in operation 301 may havean aspect ratio of at least about 2:1, at least about 3:1, at leastabout 4:1, at least about 6:1, at least about 10:1, at least about 30:1,or higher. The feature may also have a dimension near the opening, e.g.,an opening diameter or line width of between about 5 nm to 500 nm, forexample between about 25 nm and about 300 nm. Disclosed methods may beperformed on substrates with features having an opening less than about20 nm.

A via, trench or other recessed feature may be referred to as anunfilled feature or a feature. According to various embodiments, thefeature profile may narrow gradually and/or include an overhang at thefeature opening. A re-entrant profile is one that narrows from thebottom, closed end, or interior of the feature to the feature opening. Are-entrant profile may be generated by asymmetric etching kineticsduring patterning and/or the overhang due to non-conformal film stepcoverage in the previous film deposition, such as deposition of adiffusion barrier. In various examples, the feature may have a widthsmaller in the opening at the top of the feature than the width of themiddle and/or bottom of the feature.

In operation 304, the substrate is exposed to a modification gas for aduration sufficient to modify at least a surface of the substrate.Etching chemistry is introduced into the chamber in operation 304. Asdescribed herein, in operations where materials are introduced into thechamber, in some embodiments involving atomic layer etch using a plasma,the reactor or chamber may be stabilized by introducing the chemistryinto the chamber prior to processing the substrate or wafer. Stabilizingthe chamber may use the same flow rates, pressure, temperatures, andother conditions as the chemistry to be used in the operation followingthe stabilization. In some embodiments, stabilizing the chamber mayinvolve different parameters. In some embodiments, a carrier gas, suchas N₂, Ar, Ne, He, and combinations thereof, is continuously flowedduring operation 304. In some embodiments, a carrier gas is only usedduring removal. The carrier gas may be used as a purge gas in someoperations as described below.

The modification operation forms a thin, reactive surface layer with athickness that is more easily removed than the un-modified material inthe subsequent removal operation. In a modification operation, asubstrate may be chlorinated by introducing chlorine into the chamber.Chlorine is used as an example etchant species in disclosed embodiments,but it will be understood that in some embodiments, a different etchinggas is introduced into the chamber. The etching gas may be selecteddepending on the type and chemistry of the substrate to be etched. Insome embodiments, a plasma may be ignited and chlorine reacts with thesubstrate for the etching process. In some embodiments, chlorine mayreact with the substrate or may be adsorbed onto the surface of thesubstrate. In various embodiments, chlorine is introduced into thechamber in a gaseous form and may be optionally accompanied by a carriergas which may be any of those described above. The species generatedfrom a chlorine plasma can be generated directly by forming a plasma inthe process chamber housing the substrate or they can be generatedremotely in a process chamber that does not house the substrate, and canbe supplied into the process chamber housing the substrate. In someembodiments, a plasma is not used and chlorine may be introducedthermally into the chamber.

In various embodiments, the plasma may be an inductively coupled plasmaor a capacitively coupled plasma. An inductively coupled plasma may beset at a plasma between about 50 W and about 2000 W. In someembodiments, a bias may be applied between about 0V and about 500V.

In various embodiments, a plasma is ignited to facilitate themodification of the substrate surface. In some embodiments, themodification gas is ignited in a remote plasma chamber to generate aplasma species which is then delivered to the process chamber where thesubstrate is housed. In some embodiments, the modification gas isignited within the process chamber.

In various embodiments, the plasma may be pulsed during operation 304.The plasma may be pulsed between an ON state at a plasma power betweenabout 50 W and about 2000 W and an OFF state at a plasma power of 0 W.In some embodiments, the plasma may be pulsed between a low state at aplasma power between about 10 W and about 100 W and a high state at aplasma power between about 900 W and about 1500 W.

Pulsing may be performed at a pulsing frequency between about 10 Hz andabout 200 Hz. The duty cycle of the plasma pulsing for the modificationgas may be between about 1% and about 20%. It will be understood thatpulsing may involve repetitions of periods, each of which may last aduration T. The duration T includes the duration for pulse ON time (theduration for which the plasma is in an ON state) and the duration forOFF time (the duration from which the plasma is in an OFF state) duringa given period. The pulse frequency will be understood as 1/T. Forexample, for a pulsing period T=100 μs, frequency is 1/T=1/100 μs, or 10kHz. The duty cycle or duty ratio is the fraction or percentage in aperiod T during which the energy source is in the ON state such thatduty cycle or duty ratio is pulse ON time divided by T. For example, fora pulsing period T=100 μs, if a pulse ON time is 70 μs (such that theduration for which the energy source is in an ON state in a period is 70μs) and a pulse OFF time is 30 μs (such that the duration for which theenergy source is in an OFF state in a period is 30 μs), the duty cycleis 70%.

FIG. 4H provides examples of various duty cycles that may be used forALE cycles, including 3%, 10%, 40%, and 100% (100% being ALE performedwith sufficient synergy but at low continuous energy). The corresponding“ON” times for when Ar is turned on is provided in the schematic in FIG.4H.

In some embodiments, plasma is pulsed to allow higher energy to bedelivered to the modification gas. In some embodiments, plasma may bepulsed to allow the apparatus used to generate the plasma to operate atcertain conditions addressing the limitations of the apparatus. Forexample, for apparatuses that are unable to deliver plasma power for ashort, continuous duration, separating a dose which would be deliveredin a short, continuous duration into multiple pulses over a longerperiod of time such that the plasma ON time overall is the same as theshort, continuous duration eases delivery of the plasma power sufficientto modify most or all of the active sites on a substrate surface. Forexample, if the minimum amount of time needed for chlorine to modify asilicon surface continuously is 400 milliseconds, but the apparatus isincapable of delivering the chlorine gas and plasma power for that shortof a continuous duration, the 400 millisecond duration can be deliveredover 2 seconds using continuous chlorine gas flow and four cycles of 100ms pulse of plasma power and 400 ms of no plasma power.

In operation 306, the process chamber is optionally purged to removeexcess modification gas molecules that did not modify the substratesurface. In a purge operation, non-surface-bound active chlorine speciesmay be removed from the process chamber. This can be done by purgingand/or evacuating the process chamber to remove the active species,without removing the adsorbed layer. The species generated in a chlorineplasma can be removed by simply stopping the plasma and allowing theremaining species decay, optionally combined with purging and/orevacuation of the chamber. Purging can be done using any inert gas suchas N₂, Ar, Ne, He and their combinations.

In operation 308 a, an activation gas is delivered to the substrate andan activation source is used to generate activated species from theactivation gas, the activated species used to remove the modifiedsurface. In operation 308 a, the substrate is exposed to high energydoses of the activated species, which may be delivered by pulsing anenergy source such as RF plasma power, bias power, photons, or otherenergy source to etch the substrate. In some embodiments, more than onehigh energy dose is provided during operation 308 a in one ALE cycle.The high energy dose is provided with an energy greater than thethreshold energy to sputter the modified surface and for a durationinsufficient to remove the modified surface using a single energy dose.The activation gas may be an inert gas or noble gas, such as argon,helium, neon, krypton, xenon, or combinations thereof. In someembodiments, the energy of a single high energy dose is at least two toat least fifteen times greater than the sputter threshold energy. Forexample, in some embodiments, for etching silicon using disclosedembodiments, the high energy dose is provided at a bias power of atleast 150 eV, or at least 500 eV, or at least 1000 eV, or between 100 eVand about 1500 eV as compared to an example threshold sputter bias powerof 65V.

In some embodiments, one or more energy sources are pulsed, while one ormore energy sources are delivered continuously. For example, in someembodiments, RF plasma power is continuous while bias power is pulsed.In some embodiments, RF plasma power is pulsed and bias power is pulsed.In some embodiments, RF plasma power is pulsed and bias power iscontinuous. In various embodiments, where power is pulsed, pulsing maybe performed between an ON state and OFF state, or between a low stateand high state.

Pulsing conditions for plasma power and bias power, including thefrequency and duty cycle, depend on the material to be etched. The belowranges may be used for etching silicon using chlorine as a modificationgas. For RF plasma power, when pulsed between ON state and OFF state,the power during the ON state may be between about 50 W and about 900 W.For RF plasma power, when pulsed between a low and high power, the powerduring high power may be between about 900 W and about 1500 W and thepower during low power may be between about 10 W and about 100 W. Forbias power, when pulsed between ON state and OFF state, the bias powermay be about 10 to about 20 times higher than the bias power for lowenergy ALE. For etching silicon, the bias power for the ON state may bebetween about 100V and about 1500V for duty cycles between about 1% andabout 10%. For bias power, when pulsed between high power and low power,the bias power for high power may be between about 500V and about 1500Vfor duty cycles between about 1% and about 10%, and the low power may bebetween about 100V and about 300V for duty cycles between about 1% andabout 10%. In some embodiments, the bias and the RF plasma power arepulsed at least about 100 times during one ALE cycle.

In one example, the following process conditions may be used for etchingsilicon:

TABLE 1 Example Process Conditions for High Energy ALE of SiliconModification Removal Gas Chemistry Chlorine Argon Plasma Plasma Power50-900 W 0 W to 900 W Conditions Continuous or Continuous Pulsed PulsedPlasma Duty Cycle: 1-10% Frequency: 200 Hz Bias Bias Power 0 V 0 V to1500 V Conditions Continuous or No bias Pulsed Bias Pulsed Bias DutyCycle: 1-10% Frequency: 200 Hz Synchronous with Pulsed Plasma ChamberPressure 5 mTorr-1 Torr 5 mTorr-200 mTorr Conditions Substrate 0°-120°C. 0° C.-120° C. Temperature

In some embodiments, RF plasma power is continuous while bias power ispulsed between an ON state and OFF state. In some embodiments, RF plasmapower is continuous while bias power is pulsed between a high power andlow power. In some embodiments, RF plasma power is pulsed between an ONstate and OFF state while bias power is pulsed between an ON state andOFF state. In some embodiments, RF plasma power is pulsed between a highpower and a low power while bias power is pulsed between an ON state andOFF state. In some embodiments, RF plasma power is pulsed between an ONstate and OFF state while bias power is pulsed between a high power andlow power. In some embodiments, RF plasma power is pulsed between a highpower and a low power while bias power is pulsed between a high powerand low power. In some embodiments, the high bias power may be up to themaximum bias power for providing enough energy to remove the modifiedsurface without sputtering, and the low bias power may be as low as theminimum bias power for providing enough energy to remove the modifiedsurface for a given RF plasma power and duty cycle.

In some embodiments, pulsing of RF power and bias power may besynchronized, such that RF power is on when bias power is on, and RFpower is off when bias power is off, or RF power is on when bias poweris high, and RF power is off when bias power is low, or RF power is highwhen bias power is on, and RF power is low when bias power is off, or RFpower is high when bias power is high, and RF power is low when biaspower is low.

In some embodiments, pulsing of RF power and bias power may beasynchronous, such that RF power is off when bias power is on, and RFpower is on when bias power is off, or RF power is off when bias poweris high, and RF power is on when bias power is low, or RF power is lowwhen bias power is on, and RF power is high when bias power is on, or RFpower is low when bias power is high, and RF power is high when biaspower is low. In some embodiments, the frequency of pulsing RF power andfrequency of pulsing bias power are the same. In some embodiments, thefrequency of pulsing RF power and frequency of pulsing bias power aredifferent.

Pulsing may be performed at a pulsing frequency between about 10 Hz andabout 200 Hz such as about 200 Hz. The duty cycle of the plasma pulsingfor the activation gas may be between about 1% and about 10%. In variousembodiments, reducing the duty cycle increases the bias window by rangeand magnitude, such that a lower duty cycle results in a wider biaswindow and tolerance of greater bias power applied to the substrate.

For FIG. 3B, in operation 308 b, the modified surface is exposed to ahigh energy energetic particle to etch the modified surface. Theenergetic particle may have ion energy greater than the average surfacebinding energy of an underlying unmodified surface of the material to beetched. The high energy energetic particle may be delivered to thesubstrate in pulses such as described above with respect to operation308 a. In some embodiments, the energetic particle does notsignificantly sputter the underlying unmodified material. For example,the amount of the underlying unmodified material sputtered duringremoval by the energetic particle is less than about 10% of the totalamount of material removed by the energetic particle in one cycle.

In various embodiments, operation 308 b involves exposing the modifiedsurface for a duration which would be insufficient to remove at least80% of the modified surface if exposed to low ion energy.

In operation 310, the chamber is optionally purged to remove excessactivation gas and reaction byproducts from the removal operation ofoperation 308 a or 308 b.

In operation 312, operations 304-310 are optionally repeated in cycles.In various embodiments, the modification and removal operations may berepeated in cycles, such as about 1 cycle to about 200 cycles, or about1 cycle to about 150 cycles, or about 1 cycle to about 70 cycles, orabout 1 cycle to about 40 cycles, or about 1 to about 30 cycles, orabout 1 to about 20 cycles. Any suitable number of ALE cycles may beincluded to etch a desired amount of film. In some embodiments, ALE isperformed in cycles to etch about 1 Å to about 50 Å of the surface ofthe layers on the substrate. In some embodiments, cycles of ALE etchbetween about 2 Å and about 50 Å of the surface of the layers on thesubstrate.

Examples of various timing schematic diagrams are depicted in FIGS.4A-4G. For these figures, while RF plasma is depicted as being offduring surface modification, in various embodiments plasma is turned onduring surface modification. In all of the examples in FIGS. 4A-4G,modification gas is turned on and constant during surface modification,and off during purge phases and removal; removal gas is turned on andconstant during removal, and off during purge phases and removal. Whilenot depicted, it will be understood that a carrier gas may becontinuously flowed during the etch cycles. In some embodiments, thepurge phase gas is the same as the removal gas and the removal gas maythus be turned on during the purge phase while no plasma or bias poweris delivered (not shown).

FIG. 4A shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between ON and OFF during theremoval operation while the RF plasma is constant during the removaloperation. While only four ON pulses are depicted for the bias powerduring removal in one ALE cycle, multiple pulses may be used and withvarious duty cycle, such as between 1% and 10%.

FIG. 4B shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between low and high powerduring the removal operation while the RF plasma is constant during theremoval operation. While only four high power pulses are depicted forthe bias power during removal in one ALE cycle, multiple pulses may beused and with various duty cycle, such as between 1% and 10%.

FIG. 4C shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between ON and OFF during theremoval operation while the RF plasma is also pulsed between ON and OFFduring the removal operation. While only four ON pulses are depictedduring removal in one ALE cycle, multiple pulses may be used and withvarious duty cycle, such as between 1% and 10%. In this example, RFpulsing and bias power pulsing are synchronized with the same frequencyand duty cycle.

FIG. 4D shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between high and low powerduring the removal operation while the RF plasma is also pulsed betweenON and OFF during the removal operation. While only four pulses aredepicted during removal in one ALE cycle, multiple pulses may be usedand with various duty cycle, such as between 1% and 10%. In thisexample, RF pulsing and bias power pulsing are synchronized with thesame frequency and duty cycle.

FIG. 4E shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between ON and OFF during theremoval operation while the RF plasma is also pulsed between high andlow powers during the removal operation. While only four pulses aredepicted during removal in one ALE cycle, multiple pulses may be usedand with various duty cycle, such as between 1% and 10%. In thisexample, RF pulsing and bias power pulsing are synchronized with thesame frequency and duty cycle.

FIG. 4F shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between high and low powersduring the removal operation while the RF plasma is also pulsed betweenhigh and low powers during the removal operation. While only four pulsesare depicted during removal in one ALE cycle, multiple pulses may beused and with various duty cycle, such as between 1% and 10%. In thisexample, RF pulsing and bias power pulsing are synchronized with thesame frequency and duty cycle.

FIG. 4G shows two etch cycles of surface modification, purge, removal,and purge where the bias power is pulsed between ON and OFF during theremoval operation while the RF plasma is also pulsed between ON and OFFduring the removal operation. While only four bias power pulses (andonly three RF plasma pulses) are depicted during removal in one ALEcycle, multiple pulses may be used and with various duty cycle, such asbetween 1% and 10%. In this example, RF pulsing and bias power pulsingare asynchronous, such that bias power is on when RF plasma is off andbias power is off when RF plasma is on, but with the same frequency.

FIGS. 4A-4G provide only examples of timing of pulses in various pulsedALE embodiments. It will be understood that many variations may be usedin certain disclosed embodiments of pulsed ALE.

Provided herein are embodiments for achieving etch selectivity. Forexample, the etch selectivity may depend on the material to be etched,the removal gas and modification gases used, and the bias power used forthe pulses during the ON state, such that higher selectivity between twomaterials may be observed at lower bias power while lower selectivitybetween two materials may be observed at higher bias power. Sincedisclosed embodiments expand the bias window for operating self-limitingpulsed ALE, this allows one to tailor the etch selectivity of onematerial compared to another using a variety of bias powers duringpulsed ALE to obtain the desired etch characteristics and, in someembodiments, feature profile.

Apparatus

Inductively coupled plasma (ICP) reactors which, in certain embodiments,may be suitable for atomic layer etching (ALE) operations are nowdescribed. Such ICP reactors have also described in U.S. PatentApplication Publication No. 2014/0170853, filed Dec. 10, 2013, andtitled “IMAGE REVERSAL WITH AHM GAP FILL FOR MULTIPLE PATTERNING,”hereby incorporated by reference in its entirety and for all purposes.Although ICP reactors are described herein, in some embodiments, itshould be understood that capacitively coupled plasma reactors may alsobe used. In some embodiments, an electron cyclotron resonance plasma maybe used.

FIG. 5 schematically shows a cross-sectional view of an inductivelycoupled plasma etching apparatus 500 appropriate for implementingcertain embodiments herein, an example of which is a Kiyo™ reactor,produced by Lam Research Corp. of Fremont, Calif. The inductivelycoupled plasma apparatus 500 includes an overall process chamber 501structurally defined by chamber walls 501 and a window 511. The chamberwalls 501 may be fabricated from stainless steel or aluminum. The window511 may be fabricated from quartz or other dielectric material. Anoptional internal plasma grid 550 divides the overall processing chamber501 into an upper sub-chamber 502 and a lower sub-chamber 503. In mostembodiments, plasma grid 550 may be removed, thereby utilizing a chamberspace made of sub-chambers 502 and 503. A chuck 517 is positioned withinthe lower sub-chamber 503 near the bottom inner surface. The chuck 517is configured to receive and hold a semiconductor wafer 519 upon whichthe etching and deposition processes are performed. The chuck 517 can bean electrostatic chuck for supporting the wafer 519 when present. Insome embodiments, an edge ring (not shown) surrounds chuck 517, and hasan upper surface that is approximately planar with a top surface of awafer 519, when present over chuck 517. The chuck 517 also includeselectrostatic electrodes for chucking and dechucking the wafer. A filterand DC clamp power supply (not shown) may be provided for this purpose.Other control systems for lifting the wafer 519 off the chuck 517 canalso be provided. The chuck 517 can be electrically charged using an RFpower supply 523. The RF power supply 523 is connected to matchingcircuitry 521 through a connection 527. Bias power may be delivered tochuck 517 to bias the substrate. In various embodiments, the bias powermay be set to a value between 0V (no bias) and about 2000V, or between0V and 1800V, or between 0V and 1500V, or between 500V and about 1500V.The matching circuitry 521 is connected to the chuck 517 through aconnection 525. In this manner, the RF power supply 523 is connected tothe chuck 517.

Elements for plasma generation include a coil 533 is positioned abovewindow 511. In some embodiments, a coil is not used in disclosedembodiments. The coil 533 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil533 shown in FIG. 5 includes three turns. The cross-sections of coil 533are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “*” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 541configured to supply RF power to the coil 533. In general, the RF powersupply 541 is connected to matching circuitry 539 through a connection545. The matching circuitry 539 is connected to the coil 533 through aconnection 543. In this manner, the RF power supply 541 is connected tothe coil 533. The RF power supply 541 may be configured to be pulsed ata frequency between 10 Hz and 200 Hz using a duty cycle between 1% andabout 20% during the modification operation, and/or pulsed at afrequency between 10 Hz and 200 Hz using a duty cycle between 1% andabout 20% during the removal operation for an ALE cycle. An optionalFaraday shield 549 is positioned between the coil 533 and the window511. The Faraday shield 549 is maintained in a spaced apart relationshiprelative to the coil 533. The Faraday shield 549 is disposed immediatelyabove the window 511. The coil 533, the Faraday shield 549, and thewindow 511 are each configured to be substantially parallel to oneanother. The Faraday shield may prevent metal or other species fromdepositing on the dielectric window of the plasma chamber 501.

Process gases (e.g. chlorine, argon, oxygen, etc.) may be flowed intothe processing chamber 501 through one or more main gas flow inlets 560positioned in the upper chamber 502 and/or through one or more side gasflow inlets 570. Likewise, though not explicitly shown, similar gas flowinlets may be used to supply process gases to a capacitively coupledplasma processing chamber. A vacuum pump, e.g., a one or two stagemechanical dry pump and/or turbomolecular pump 540, may be used to drawprocess gases out of the process chamber 501 and to maintain a pressurewithin the process chamber 501. For example, the pump may be used toevacuate the chamber 501 during a purge operation of ALE. Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the processing chamber 501 so as to selectively controlapplication of the vacuum environment provided by the vacuum pump. Thismay be done employing a closed-loop-controlled flow restriction device,such as a throttle valve (not shown) or a pendulum valve (not shown),during operational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus, one or more process gases may besupplied through the gas flow inlets 560 and/or 570. In certainembodiments, process gas may be supplied only through the main gas flowinlet 560, or only through the side gas flow inlet 570. In some cases,the gas flow inlets shown in the figure may be replaced more complex gasflow inlets, one or more showerheads, for example. The Faraday shield549 and/or optional grid 550 may include internal channels and holesthat allow delivery of process gases to the chamber 501. Either or bothof Faraday shield 549 and optional grid 550 may serve as a showerheadfor delivery of process gases. In some embodiments, a liquidvaporization and delivery system may be situated upstream of the chamber501, such that once a liquid reactant or precursor is vaporized, thevaporized reactant or precursor is introduced into the chamber 501 via agas flow inlet 560 and/or 570. Example liquid precursors include SiCl₄and silicon amides.

Radio frequency power is supplied from the RF power supply 541 to thecoil 533 to cause an RF current to flow through the coil 533. The RFcurrent flowing through the coil 533 generates an electromagnetic fieldabout the coil 533. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 502. The physical and chemicalinteractions of various generated ions and radicals with the wafer 519selectively etch features of and deposit layers on the wafer.

If the plasma grid is used such that there is both an upper sub-chamber502 and a lower sub-chamber 503, the inductive current acts on the gaspresent in the upper sub-chamber 502 to generate an electron-ion plasmain the upper sub-chamber 502. The optional internal plasma grid 550limits the amount of hot electrons in the lower sub-chamber 503. In someembodiments, the apparatus is designed and operated such that the plasmapresent in the lower sub-chamber 503 is an ion-ion plasma.

Both the upper electron-ion plasma and the lower ion-ion plasma maycontain positive and negative ions, though the ion-ion plasma will havea greater ratio of negative ions to positive ions. Volatile etchingand/or deposition byproducts may be removed from the lower sub-chamber503 through port 522. The chuck 517 disclosed herein may operate attemperatures ranging between about −200° C. and about 600° C. or betweenabout −20° C. and about 250° C. for processing a substrate to etchtantalum, the chuck 517 may be set at a temperature less than about 0°C. The temperature will depend on the process operation and specificrecipe and the tool used.

Chamber 501 may be coupled to facilities (not shown) when installed in aclean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to chamber 501, wheninstalled in the target fabrication facility. Additionally, chamber 501may be coupled to a transfer chamber that allows robotics to transfersemiconductor wafers into and out of chamber 501 using typicalautomation.

In some embodiments, a system controller 530 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a processing chamber. The system controller 530 mayinclude one or more memory devices and one or more processors. In someembodiments, the apparatus includes a switching system for controllingflow rates and durations when disclosed embodiments are performed. Insome embodiments, the apparatus may have a switching time of up to about500 ms, or up to about 750 ms. Switching time may depend on the flowchemistry, recipe chosen, reactor architecture, and other factors.

In some implementations, a controller 530 is part of a system, which maybe part of the above-described examples. Such systems can comprisesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer substrate support, a gasflow system, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller 530, depending on the processingparameters and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller 530 may be defined as electronicshaving various integrated circuits, logic, memory, and/or software thatreceive instructions, issue instructions, control operation, enablecleaning operations, enable endpoint measurements, and the like. Theintegrated circuits may include chips in the form of firmware that storeprogram instructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer. In someembodiments, controller 530 may be used to determine a window fortemperature for the modification operation of ALE, or to determine awindow for process conditions for the removal operation of ALE, or both.

The controller 530, in some implementations, may be a part of or coupledto a computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller 530 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thecontroller 530 may be distributed, such as by comprising one or morediscrete controllers that are networked together and working towards acommon purpose, such as the processes and controls described herein. Anexample of a distributed controller for such purposes would be one ormore integrated circuits on a chamber in communication with one or moreintegrated circuits located remotely (such as at the platform level oras part of a remote computer) that combine to control a process on thechamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

FIG. 6 depicts a semiconductor process cluster architecture with variousmodules that interface with a vacuum transfer module 638 (VTM). Thearrangement of transfer modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock 630, also known as aloadlock or transfer module, is shown in VTM 638 with four processingmodules 620 a-620 d, which may be individual optimized to performvarious fabrication processes. By way of example, processing modules 620a-620 d may be implemented to perform substrate etching, deposition, ionimplantation, wafer cleaning, sputtering, and/or other semiconductorprocesses. One or more of the substrate etching processing modules (anyof 620 a-620 d) may be implemented as disclosed herein, i.e., forintroducing a modification gas, for introducing a removal gas, and othersuitable functions in accordance with the disclosed embodiments. Airlock630 and process module 620 may be referred to as “stations.” Eachstation has a facet 636 that interfaces the station to VTM 638. Insideeach facet, sensors 1-18 are used to detect the passing of wafer 626when moved between respective stations.

Robot 622 transfers wafer 626 between stations. In one embodiment, robot622 has one arm, and in another embodiment, robot 622 has two arms,where each arm has an end effector 624 to pick wafers such as wafer 626for transport. Front-end robot 632, in atmospheric transfer module (ATM)640, is used to transfer wafers 626 from cassette or Front OpeningUnified Pod (FOUP) 634 in Load Port Module (LPM) 642 to airlock 630.Module center 628 inside process module 620 is one location for placingwafer 626. Aligner 644 in ATM 640 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs634 in the LPM 642. Front-end robot 632 transfers the wafer from theFOUP 634 to an aligner 644, which allows the wafer 626 to be properlycentered before it is etched or processed. After being aligned, thewafer 626 is moved by the front-end robot 632 into an airlock 630.Because airlock modules have the ability to match the environmentbetween an ATM and a VTM, the wafer 626 is able to move between the twopressure environments without being damaged. From the airlock module630, the wafer 626 is moved by robot 622 through VTM 638 and into one ofthe process modules 620 a-320 d. In order to achieve this wafermovement, the robot 622 uses end effectors 624 on each of its arms. Oncethe wafer 626 has been processed, it is moved by robot 622 from theprocess modules 620 a-320 d to an airlock module 630. From here, thewafer 626 may be moved by the front-end robot 632 to one of the FOUPs634 or to the aligner 644.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 5 may be implemented with the toolin FIG. 6.

EXPERIMENTAL Experiment 1

An experiment was conducted on silicon on insulator material on asubstrate by exposing the substrate to 40 cycles of pulsed atomic layeretching, each cycle including: 200 sccm chlorine dose for modificationat 40 mTorr, pulsed at 100 Hz frequency; purge using argon; 400 sccmhelium flow with 300 W plasma using pulsed bias (ON/OFF) at 100 Hzfrequency; purge using argon. The etch per cycle was determined for eachtrial, each trial using a different bias power for the ON state of thebias ranging from 100 to 500 in 50V increments. The bias power wasplotted against etch per cycle in angstroms in FIG. 7, which shows asaturated etch rate with a self-limiting regime at a high bias powerbetween 300V and 500V, which is substantially higher than aself-limiting bias power in continuous ALE. The Y-axis depicted in FIG.7 is a linear scale.

Experiment 2

An experiment was conducted for determining etch per cycle for amorphoussilicon and silicon oxide material on a substrate. Both amorphoussilicon and silicon oxide were exposed to 70 cycles of pulsed atomiclayer etching using helium as the removal gas, each cycle including: 180sccm chlorine with 180 sccm of helium for modification at 20 mTorr,pulsed at 100 Hz frequency with no bias; purge using helium; 400 sccmhelium flow with 0 W plasma power using pulsed bias (ON/OFF) at 100 Hzfrequency; purge using helium. The etch per cycle was determined atvarious bias powers for the ON state of the bias, ranging from 100V to500V in 100V increments. The bias power was plotted against etch percycle in angstroms in FIG. 8A, which shows a higher etch per cycle ofamorphous silicon (triangles) than of silicon oxide (circles). TheY-axis depicted in FIG. 8A is a linear scale. The etch selectivity ofamorphous silicon to silicon oxide was calculated and depicted in FIG.8B, showing higher selectivity at lower bias power and lower selectivityat high bias power. These results suggest that the broader range of biaspower can be tailored to achieve etch selectivity using pulsed ALE.

Experiment 3

An experiment was conducted for determining etch per cycle for amorphoussilicon and silicon oxide material on a substrate. Both amorphoussilicon and silicon oxide were exposed to 200 cycles of pulsed atomiclayer etching using argon as the removal gas, each cycle including: 180sccm chlorine with 180 sccm helium for modification at 20 mTorr, pulsedat 100 Hz frequency with no bias and 200 W plasma power; purge usingargon; 400 sccm argon flow with 0 W plasma power using pulsed bias(ON/OFF) at 100 Hz frequency; purge using argon. The etch per cycle wasdetermined at various bias powers for the ON state of the bias, rangingfrom 200V to 400V in 25V or 50V increments. The bias power was plottedagainst etch per cycle in angstroms in FIG. 9A, which shows a higheretch per cycle of amorphous silicon (triangles) than of silicon oxide(circles). The Y-axis depicted in FIG. 9A is a linear scale. The etchselectivity of amorphous silicon to silicon oxide was calculated anddepicted in FIG. 9B, showing higher selectivity at lower bias power andlower selectivity at high bias power. These results suggest that thebroader range of bias power can be tailored to achieve etch selectivityusing pulsed ALE.

Experiment 4

An experiment was conducted on patterned substrates using pulsed ALEwhere the removal gas used was helium. The pattern of the substrateincluded both iso and dense structures, the iso structures having afeature with of 80 nm and the dense structures having a feature with ofabout 5 nm near the opening of the feature, with feature depths being onthe order of 60 nm to 80 nm. The substrate was exposed to multiplecycles of pulsed ALE at a substrate temperature of 120° C., each cycleincluding: chlorine dose with plasma, purge with helium, helium removalgas exposure with plasma and pulsed bias at 25% duty cycle for 3 secondsper exposure between 0V and 65V bias power, and purge with helium. Thepitch loading percent was calculated for various trenches having a rangeof critical dimensions, and the results are depicted in FIG. 10A. Asshown, as trench size increases, pitch loading decreases.

A pattern of similar structure was exposed to multiple cycles of pulsedALE at a substrate temperature of 120° C., each cycle including:chlorine dose with plasma, purge with helium, helium removal gasexposure with plasma and pulsed bias at 10% duty cycle for 3 seconds perexposure between 0V and 150V bias power, and purge with helium. Thepitch loading percent was calculated for various trenches having a rangeof critical dimensions, and the results are depicted in FIG. 10B. Asshown, as trench size increases, pitch loading decreases.

Images of the substrates were generated, which showed that for trencheshaving a feature opening less than 10 nm, higher helium bias pulsedbetween 0V and 150V using 10% duty cycle achieved more similar etchingdepths for each feature across the substrate than substrates exposed tolow helium bias pulsed between 0V and 65V using 25% duty cycle.

Experiment 5

FIG. 11 shows a comparison of etch per cycle vs bias during removaloperation for three different curves. Curve 1002 shows an example ofetch per cycle when ALE is performed with 3% duty cycle pulsing duringthe removal operation using a 2-second exposure time. Curve 1101 showsan example of etch per cycle with ALE is performed with 10% duty cyclepulsing during the removal operation using a 2 second exposure time.These are compared with curve 1103 where ALE is performed withoutpulsing (e.g., duty cycle of 100%) with a 7-second exposure time duringremoval. As shown, the pulsed embodiments saturate (10% duty cyclesaturates at about 900 eV, and 3% duty cycle saturates at about 1500 eV)while the data provided for the non-pulsed embodiment does not have aparticular saturation bias voltage.

Experiment 6

FIG. 12A shows an example of experimental data collected for etch percycle versus bias voltage in continuous exposure during removal. Arrow1201 shows an example of an ALE window of voltage where etch per cycleis saturated.

FIG. 12B shows an example of etch per cycle versus time in continuousALE of silicon. In comparison, literature shows that etch amounts forion beam in an etch reactor as a function of duration of argon exposureinvolves an increase in etch amount between 100 to 300 seconds of argonexposure, followed by a relatively horizontal slope of etch amount up toabout 650 seconds, and a slight increase in some cases for exposure ofargon beyond 700 seconds.

Experiment 7

FIG. 13 shows complete removal of ion energy dependent on “ON” time ofargon ions.

FIG. 14A shows the ALE window for various ON times on silicon substrateusing chlorine as a modification gas and argon as a removal gas,assuming the flux rate is F=F₀(1+a*V_(bias){circumflex over ( )}1.5),where F₀ is determined from experimental data. For example, curve 1401represents the normalized etch per cycle where each pulse is 0.06seconds, curve 1402 represents the normalized etch per cycle where eachpulse is 0.2 seconds, curve 1403 represents the normalized etch percycle where each pulse is 0.5 seconds, curve 1405 represents thenormalized etch per cycle where each pulse is 1 second, curve 1407represents the normalized etch per cycle where each pulse is 2 seconds,curve 1408 represents the normalized etch per cycle where each pulse is3 seconds, and curve 1409 represents the normalized etch per cycle whereeach pulse is 7 seconds. Line 1410 shows the amount at which one layeris etched.

FIG. 14B shows an example fit simulation to data showing the etch percycle for pulsed ALE that can allow complete removal using thesynergistic effect of ALE using certain argon ON times. These resultssuggest that even at much higher durations of “on” time during removal,pulsed ALE can allow complete removal using a higher etch rate per cyclewithout substantial sputtering.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

What is claimed is:
 1. An apparatus for processing a substrate, theapparatus comprising: a process chamber comprising a showerhead and asubstrate support for holding the substrate having a material, a plasmagenerator, and a controller having at least one processor and a memory,wherein the at least one processor and the memory are communicativelyconnected with one another, the at least one processor is at leastoperatively connected with flow-control hardware, and the memory storesmachine-readable instructions for: causing introduction of amodification gas to the process chamber; causing introduction of aremoval gas to the process chamber; and causing an activation source tobe pulsed during the introduction of the removal gas.
 2. The apparatusof claim 1, wherein the memory further stores machine-readableinstructions for causing a pulse frequency of the activation sourceduring the introduction of the removal gas to be between about 10 Hz andabout 200 Hz.
 3. The apparatus of claim 1, wherein the memory furtherstores machine-readable instructions for causing a duty cycle of theactivation source during the introduction of the removal gas to be lessthan 100% or between about 1% and about 20%.
 4. The apparatus of claim1, wherein the activation source is a plasma generated in the processchamber using a plasma power and the memory further storesmachine-readable instructions for causing the activation source to pulsebetween an OFF state where the plasma power is 0 W and an ON state wherethe plasma power is between about 50 W and about 900 W.
 5. The apparatusof claim 1, wherein the activation source is a plasma generated in theprocess chamber and the memory further stores machine-readableinstructions for causing the activation source to pulse between a lowplasma power and a high plasma power, the low plasma power being betweenabout 10 W and about 100 W and the high plasma power being between about900 W and about 1500 W.
 6. The apparatus of claim 1, wherein the memoryfurther stores machine-readable instructions for causing a bias to beapplied to the substrate support in pulses.
 7. The apparatus of claim 6,wherein the memory further stores machine-readable instructions forcausing the bias to be pulsed between 0V and a bias voltage betweenabout 20V and about 2000V.
 8. The apparatus of claim 6, wherein thememory further stores machine-readable instructions for causing the biasto be pulsed at a same pulsing frequency as the activation source. 9.The apparatus of claim 6, wherein the memory further storesmachine-readable instructions for causing the bias to be pulsed at asame pulsing duty cycle as the activation source.
 10. An apparatus forprocessing a substrate, the apparatus comprising: a process chambercomprising a showerhead and a substrate support for holding thesubstrate having a material, a plasma generator, and a controller havingat least one processor and a memory, wherein the at least one processorand the memory are communicatively connected with one another, the atleast one processor is at least operatively connected with flow-controlhardware, and the memory stores machine-readable instructions for:causing introduction of a modification gas to the process chamber;causing introduction of a removal gas to the process chamber; andcausing radio frequency plasma power to be generated in the processchamber in two or more temporally separated pulses during theintroduction of the removal gas.
 11. The apparatus of claim 10, whereinthe memory further stores machine-readable instructions for causing apulse frequency of the radio frequency plasma power during theintroduction of the removal gas to be between about 10 Hz and about 200Hz.
 12. The apparatus of claim 10, wherein the memory further storesmachine-readable instructions for causing a duty cycle of the radiofrequency plasma power during the introduction of the removal gas to beless than 100% or between about 1% and about 20%.
 13. The apparatus ofclaim 10, wherein the memory further stores machine-readableinstructions for causing the radio frequency plasma power to pulsebetween an OFF state where a plasma power is 0 W and an ON state wherethe plasma power is between about 50 W and about 900 W.
 14. Theapparatus of claim 10, wherein the memory further storesmachine-readable instructions for causing the radio frequency plasmapower to pulse between a low plasma power and a high plasma power, thelow plasma power being between about 10 W and about 100 W and the highplasma power being between about 900 W and about 1500 W.
 15. Theapparatus of claim 10, wherein the memory further storesmachine-readable instructions for causing a bias to be applied to thesubstrate support in pulses.
 16. The apparatus of claim 15, wherein thememory further stores machine-readable instructions for causing the biasto be pulsed between 0V and a bias voltage between about 20V and about2000V.
 17. The apparatus of claim 15, wherein the memory further storesmachine-readable instructions for causing the bias to be pulsed betweena low bias voltage between about 50V and about 300V and a high biasvoltage between about 500V and about 2000V.
 18. The apparatus of claim15, wherein the memory further stores machine-readable instructions forcausing the bias to be pulsed at a same pulsing frequency as the radiofrequency plasma power.
 19. The apparatus of claim 15, wherein thememory further stores machine-readable instructions for causing the biasto be pulsed at a same pulsing duty cycle as the radio frequency plasmapower.
 20. An apparatus for processing a substrate, the apparatuscomprising: a process chamber comprising a showerhead and a substratesupport for holding the substrate having a material, a plasma generator,and a controller having at least one processor and a memory, wherein theat least one processor and the memory are communicatively connected withone another, the at least one processor is at least operativelyconnected with flow-control hardware, and the memory storesmachine-readable instructions for: causing introduction of amodification gas to the process chamber; causing introduction of aremoval gas to the process chamber; and causing a bias power to beapplied to the substrate support in two or more temporally separatedpulses to the substrate during the introduction of the removal gas. 21.The apparatus of claim 20, wherein the memory further storesmachine-readable instructions for causing a pulse frequency of the biaspower during the introduction of the removal gas to be between about 10Hz and about 200 Hz.
 22. The apparatus of claim 20, wherein the memoryfurther stores machine-readable instructions for causing a duty cycle ofthe bias power during the introduction of the removal gas to be lessthan 100% or between about 1% and about 20%.
 23. The apparatus of claim20, wherein the memory further stores machine-readable instructions forcausing the bias power to pulse between an OFF state where the biaspower is 0V and an ON state where the bias power is between about 20Vand about 2000V.
 24. The apparatus of claim 20, wherein the memoryfurther stores machine-readable instructions for causing the bias powerto pulse between a low bias power and a high bias power, the low biaspower being between about 50V and about 300V and the high bias powerbeing between about 500V and about 2000V.
 25. The apparatus of claim 20,wherein the memory further stores machine-readable instructions forcausing a plasma to be ignited by applying a plasma power in pulsesduring the introduction of the removal gas.
 26. The apparatus of claim25, wherein the memory further stores machine-readable instructions forcausing the plasma power to be pulsed between 0 W and the plasma powerbetween about 50 W and about 900 W.
 27. The apparatus of claim 25,wherein the memory further stores machine-readable instructions forcausing the plasma power to be pulsed at a same pulsing frequency as thebias power.
 28. The apparatus of claim 25, wherein the memory furtherstores machine-readable instructions for causing the plasma power to bepulsed at a same pulsing duty cycle as the bias power.